Pressure Control in Phacoemulsification System

ABSTRACT

A surgical system comprises a pressurized irrigation fluid source; an irrigation line fluidly coupled to the pressurized irrigation fluid source; a hand piece fluidly coupled to the irrigation line; an irrigation pressure sensor located at or along the pressurized irrigation fluid source or irrigation line; and a controller for controlling the pressurized irrigation fluid source. The controller controls the pressurized irrigation fluid source based on a reading from the irrigation pressure sensor and an estimated flow value modified by a compensation factor.

BACKGROUND OF THE INVENTION

The present invention relates to phacoemulsification surgery and moreparticularly to the control fluid flow during surgery.

The human eye functions to provide vision by transmitting light througha clear outer portion called the cornea, and focusing the image by wayof a crystalline lens onto a retina. The quality of the focused imagedepends on many factors including the size and shape of the eye, and thetransparency of the cornea and the lens. When age or disease causes thelens to become less transparent, vision deteriorates because of thediminished light which can be transmitted to the retina. This deficiencyin the lens of the eye is medically known as a cataract. An acceptedtreatment for this condition is surgical removal of the lens andreplacement of the lens function by an artificial intraocular lens(IOL).

In the United States, the majority of cataractous lenses are removed bya surgical technique called phacoemulsification. A typical surgicalinstrument suitable for phacoemulsification procedures on cataractouslenses includes an ultrasonically driven phacoemulsification hand piece,an attached hollow cutting needle surrounded by an irrigating sleeve,and an electronic control console. The hand piece is attached to thecontrol console by an electric cable and flexible tubing. Through theelectric cable, the console varies the power level transmitted by thehand piece to the attached cutting needle. The flexible tubing suppliesirrigation fluid to the surgical site and draws aspiration fluid fromthe eye through the hand piece.

During a phacoemulsification procedure, the tip of the cutting needleand the end of the irrigation sleeve are inserted into the anteriorsegment of the eye through a small incision in the eye's outer tissue.The surgeon brings the tip of the cutting needle into contact with thelens of the eye, so that the vibrating tip fragments the lens. Theresulting fragments are aspirated out of the eye through the interiorbore of the cutting needle, along with irrigation fluid provided to theeye during the procedure, and into a waste reservoir.

Throughout the procedure, irrigating fluid is infused into the eye,passing between the irrigation sleeve and the cutting needle and exitinginto the eye at the tip of the irrigation sleeve and/or from one or moreports or openings formed into the irrigation sleeve near its end. Thisirrigating fluid is critical, as it prevents the collapse of the eyeduring the removal of the emulsified lens. The irrigating fluid alsoprotects the eye tissues from the heat generated by the vibrating of theultrasonic cutting needle. Furthermore, the irrigating fluid suspendsthe fragments of the emulsified lens for aspiration from the eye.

Conventional systems employ fluid-filled bottles or bags hung from anintravenous (IV) pole as an irrigation fluid source. Irrigation flowrates, and corresponding fluid pressure at the eye, are regulated bycontrolling the height of the IV pole above the surgical site. Forexample, raising the IV pole results in a corresponding increase in headpressure and increase in fluid pressure at the eye, resulting in acorresponding increase in irrigation flow rate. Likewise, lowering theIV pole results in a corresponding decrease in pressure at the eye andcorresponding irrigation flow rate to the eye.

Aspiration flow rates of fluid from the eye are typically regulated byan aspiration pump. The pump action produces aspiration flow through theinterior bore of the cutting needle. The aspiration flow results in thecreation of vacuum at the aspiration line. The aspiration flow and/orvacuum are set to achieve the desired working effect for the lensremoval. The IV pole height and irrigation pump are regulated to achievea proper intra-ocular chamber balance in an effort to maintain arelatively consistent fluid pressure at the surgical site within theeye.

While a consistent fluid pressure in the eye is desirable during thephacoemulsification procedure, a common phenomenon during aphacoemulsification procedure arises from the varying flow rates thatoccur throughout the surgical procedure. Varying flow rates result invarying pressure losses in the irrigation fluid path from the irrigationfluid supply to the eye, thus causing changes in pressure in theanterior chamber (also referred to as Intra-Ocular Pressure or IOP).Higher flow rates result in greater pressure losses and lower IOP. AsIOP lowers, the operating space within the eye diminishes.

Another common complication during the phacoemulsification processarises from a blockage, or occlusion, of the aspirating needle. As theirrigation fluid and emulsified tissue is aspirated away from theinterior of the eye through the hollow cutting needle, pieces of tissuethat are larger than the diameter of the needle's bore may becomeclogged in the needle's tip. While the tip is clogged, vacuum pressurebuilds up within the tip. The resulting drop in pressure in the anteriorchamber in the eye when the clog is removed is known as post-occlusionsurge. This post-occlusion surge, in some cases, can cause a relativelylarge quantity of fluid and tissue to be aspirated out of the eye tooquickly, potentially causing the eye to collapse and/or causing the lenscapsule to be torn.

Various techniques have been attempted to reduce this surge, such as byventing the aspiration line or otherwise limiting the buildup ofnegative pressure in the aspiration system. However, there remains aneed for improved phacoemulsification devices, including irrigationsystems that reduce post-occlusion surge as well as maintain a stableIOP throughout varying flow conditions.

SUMMARY OF THE INVENTION

In one embodiment consistent with the principles of the presentinvention, the present invention is a surgical system comprising apressurized irrigation fluid source; an irrigation line fluidly coupledto the pressurized irrigation fluid source; a hand piece fluidly coupledto the irrigation line; an irrigation pressure sensor located at oralong the pressurized irrigation fluid source or irrigation line; and acontroller for controlling the pressurized irrigation fluid source. Thecontroller controls the pressurized irrigation fluid source based on areading from the irrigation pressure sensor and an estimated flow valuemodified by a compensation factor.

The surgical system may also include a display and a controller inputdevice. The controller input device may receive a desired intraocularpressure value and the controller may control the pressurized irrigationfluid source so as to maintain the desired intraocular pressure value.The controller input device may receive a desired intraocular pressurerange and the controller may control the pressurized irrigation fluidsource so as to maintain the desired intraocular pressure range. Thecontroller may calculate intraocular pressure of an eye based on thereading from the irrigation pressure sensor, a source pressure sensor,or the aspiration pressure sensor, or from the estimated flow valuemodified by the compensation factor. The controller may also calculatethe estimated flow value based on a reading from the irrigation pressuresensor, the source pressure sensor, and an impedance of the irrigationline.

The system may also include an aspiration line fluidly coupled to thehand piece; an aspiration pressure sensor located at or along theaspiration line; and an aspiration pump configured to draw fluid throughthe aspiration line. In such a case, the controller may calculate theestimated flow value based on a reading from the aspiration pressuresensor, a maximum pump vacuum achievable by the aspiration pump, and animpedance of the aspiration pump.

The system may also include a flexible bag holding a fluid and twoopposing plates. The flexible bag can be located between the twoopposing plates. In such a case, the controller may calculate theestimated flow value based on travel or motion of the two opposingplates.

In some embodiments, the compensation factor may be based on incisionleakage and/or sleeve compression, a needle and sleeve selected for aprocedure, or flow characteristics of the needle and sleeve combination.The controller input device may receive needle and sleeve informationand the controller uses the needle and sleeve information to select orcalculate the compensation factor. The controller input device mayreceive the compensation factor as an input from the user.

The controller may use a reading from the aspiration pressure sensor todetermine if an occlusion is present or if an occlusion break occurs. Insuch a case, the controller may control the pressurized irrigation fluidsource to accommodate for changes in fluid flow that result from theocclusion or the occlusion break. The controller may use a reading fromthe irrigation pressure sensor to determine if an occlusion is presentor if an occlusion break occurs. In such a case, the controller maycontrol the pressurized irrigation fluid source to accommodate forchanges in fluid flow that result from the occlusion or the occlusionbreak.

In other embodiments of the present invention, a surgical systemcomprises: a pressurized irrigation fluid source, the pressurizedirrigation fluid source comprising a flexible bag located between twoopposing plates, the flexible bag containing a fluid; a position sensorlocated at or on one of the two opposing plates, the position sensor fordetermining a distance between the two opposing plates; an actuator formoving at least one of the two opposing plates so as to squeeze theflexible bag; and a controller for controlling the relative movement ofthe opposing plates. The controller receives reading from the positionsensor, determines the distance between the plates, and provides anestimate of an amount of fluid in the flexible bag.

In other embodiments of the present invention, a surgical systemcomprises: a pressurized irrigation fluid source, the pressurizedirrigation fluid source comprising a flexible bag located between twoopposing plates, the flexible bag containing a fluid, a hinged platelocated on a surface of one of the two opposing plates; a sourcepressure sensor located between a face of the hinged plate and a face ofone of the two opposing plates, such that the face of the hinged platepresses the source pressure sensor against the face of one of the twoopposing plates.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the invention asclaimed. The following description, as well as the practice of theinvention, set forth and suggest additional advantages and purposes ofthe invention.

In one embodiment consistent with the principles of the presentinvention, a method of controlling a surgical system having a fluid flowpath comprises: receiving a pressure reading from an irrigation pressuresensor located along the fluid flow path; calculating an estimated fluidflow through the surgical system; modifying the estimated fluid flowwith a compensation factor; and controlling a pressurized irrigationfluid source based on the pressure reading and the estimated fluid flowas modified by the compensation factor.

In other embodiments of the present invention, the method may alsocomprise one or more of the following: receiving a desired intraocularpressure value; and controlling the pressurized irrigation fluid sourceso as to maintain the desired intraocular pressure value; receiving adesired intraocular pressure range; and controlling the pressurizedirrigation fluid source so as to maintain the desired intraocularpressure range; calculating an intraocular pressure of an eye based onthe reading from the irrigation pressure sensor; calculating anintraocular pressure of an eye based on the estimated flow valuemodified by the compensation factor; receiving a reading from anaspiration pressure sensor located along the fluid path, a maximum pumpvacuum achievable by the aspiration pump, and an impedance of theaspiration pump; and estimating flow based on a difference between thereading from the aspiration pressure sensor and the maximum pump vacuumachievable by the aspiration pump; receiving a reading from theirrigation pressure sensor, a reading from a source pressure sensor, andan impedance of the fluid flow path between the source pressure sensorand the irrigation pressure sensor; and estimating flow based on adifference between the reading from the irrigation pressure sensor andthe source pressure sensor; receiving a compensation factor from a user;receiving needle and sleeve information; and using the needle and sleeveinformation to select or calculate the compensation factor; receiving apressure reading from an aspiration pressure sensor located along thefluid path; and using the pressure reading from the aspiration pressuresensor to determine if an occlusion is present or if an occlusion breakoccurs; accommodating for changes in fluid flow that result from theocclusion or the occlusion break; receiving a pressure reading from theirrigation pressure sensor; and using the pressure reading from theirrigation pressure sensor to determine if an occlusion is present or ifan occlusion break occurs.

In other embodiments consistent with the principles of the presentinvention, a method of calculating incision leakage comprises:calculating irrigation fluid flow; calculating aspiration fluid flow;and subtracting calculated aspiration fluid flow from calculatedirrigation fluid flow; wherein calculated irrigation fluid flow andcalculated aspiration fluid flow are determined from differentialpressure measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a diagram of the components in the fluid path of aphacoemulsification system including a pressurized irrigation sourceaccording to the principles of the present invention.

FIG. 2 is a pressurized irrigation fluid source according to theprinciples of the present invention.

FIGS. 3 and 4 depict a hinged pressure sensor arrangement for apressurized irrigation fluid source according to the principles of thepresent invention.

FIG. 5 is a diagram of system components in a pressurized irrigationfluid source control system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made in detail to the exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a diagram of the components in the fluid path of aphacoemulsification system including a pressurized irrigation sourceaccording to the principles of the present invention. FIG. 1 depicts thefluid path through the eye 1145 during cataract surgery. The componentsinclude a pressurized irrigation fluid source 1105, a source pressuresensor 1110, an irrigation pressure sensor 1130, a three-way valve 1135,an irrigation line 1140, a hand piece 1150, an aspiration line 1155, anaspiration pressure sensor 1160, a vent valve 1165, a pump 1170, areservoir 1175 and a drain bag 1180. The irrigation line 1140 providesirrigation fluid to the eye 1145 during cataract surgery. The aspirationline 1155 removes fluid and emulsified lens particles from the eyeduring cataract surgery.

When irrigation fluid exits pressurized irrigation fluid source 1105, ittravels through irrigation line 1140 and into the eye 1145. Anirrigation pressure sensor 1130 measures the pressure of the irrigationfluid in irrigation line 1140. Irrigation pressure sensor 1130 may belocated anywhere along the irrigation line 1140 or irrigation fluidpath. If located close to the eye 1145, irrigation pressure sensor mayalso be incorporated into the irrigation path of the hand piece 1150. Insome instances, the irrigation line 1140 may pass through and include apath in a fluidics cassette. In this case, the irrigation pressuresensor 1130 may be located in the fluidics cassette. For purposes ofthis description, irrigation line 1140 may comprise flexible tubing, apath through a fluidics cassette, rigid tubing, or other fluidicpathways that carry irrigation fluid from pressurized irrigation fluidsource 1105 through hand piece 1150 and into eye 1145. Source pressuresensor 1110 also measures the pressure of irrigation fluid at thepressurized irrigation fluid source 1105. A three-way valve 1135 isprovided for on/off control of irrigation and to provide a path to thedrain bag 1180. Irrigation pressure sensor 1130 and source pressuresensor 1110 are implemented by any of a number of commercially availablefluid pressure sensors. Irrigation pressure sensor 1130 and/or sourcepressure sensor 1110 provides pressure information to a controller(shown in FIG. 5) that operates pressurized irrigation fluid source1105. The pressurized irrigation fluid source 1105 controls the pressureand/or flow rate of the irrigation fluid exiting it.

In some embodiments of the present invention, the pressurized irrigationfluid source 1105 includes a flexible bag that contains irrigationfluid. In this case, the bag can be squeezed to pressurize the fluid itcontains. For example, the bag may be located between two opposingplates that press together to pressurize the contents of the bag (asmore fully described in FIG. 2). In another example, a flexible bandsurrounds the bag and is tightened to squeeze the bag and pressurize itscontents. In other embodiments of the present invention, the pressurizedirrigation fluid source 1105 includes a bottle or other container thatcan be pressurized. In further embodiments of the present invention, thepressurized irrigation fluid source 1105 is pressurized using a pump ora compressed gas.

The source pressure sensor 1110 may be a single pressure sensor or anarray of pressure sensors. The source pressure sensor 1110 may contactthe pressurized irrigation fluid source 1105 to determine the pressureof its contents. For example, when the pressurized irrigation fluidsource 1105 is a flexible bag located between two opposing plates,source pressure sensor 1110 may be located on one of the plates adjacentto the bag. As the plates travel, the bag is pressurized and sourcepressure sensor 1110 measures the pressure. In this case, the sourcepressure sensor 1110 may be an array of sensors located on the plate ora single sensor located on the plate. In another example, a hingedplated may be used as more fully described in FIG. 4.

FIG. 2 depicts pressurized irrigation fluid source 1105 as a flexiblebag 1109 (e.g. an IV bag) located between two opposing plates 1106 and1107. One of the two plates 1106 or 1107 may be fixed while the otherplate travels to compress or squeeze flexible bag 1109. For example,plate 1106 may be fixed and plates 1107 may travel to compress flexiblebag 1109. In FIG. 3, plate 1106 has an array of source pressure sensors1110 located on a surface that faces the flexible bag 1109. In thismanner, a reading from each of the four depicted source pressure sensors1110 may lead to a more accurate pressure reading. In this example, areading can be taken from each of the four source pressure sensors 1110,and the readings averaged or an errant reading thrown out. In FIG. 4, asource pressure sensor 1110 (or an array of sensors) is located on plate1106 under a hinged plate 1108. The flat surface of the hinged plate1108 contacts the source pressure sensor 1110. In some cases, thesurface of the flexible bag 1109 may become wrinkled or have creaseswhen it is squeezed between plates 1106 and 1107. These wrinkles orcreases can lead to inaccurate pressure readings if a wrinkle or creaseis located at a source pressure sensor 1110. Using an array of sensorsas shown in FIG. 3 is one way to overcome this problem. Using a hingedplate 1108 is another way. When using a hinged plate 1108, a flatuniform surface always contacts source pressure sensor 1110.

FIG. 5 is a block diagram representing some components of aphacoemulsification machine. FIG. 5 shows an irrigation line 1140, anirrigation pressure sensor 1130 in, along, or associated with theirrigation line 1140, an aspiration line 1155, an aspiration pressuresensor 1160 in, along, or associated with the aspiration line 1155, ahand piece 1150, a controller 1230, a flow command input device 1210(e.g. a foot pedal), a display 1220, and an associated controller inputdevice 1240 for entering data or commands for programming the system.

The irrigation line 1140 extends between a pressurized irrigation fluidsource 1105 and the hand piece 1150 and carries fluid to the hand piece1150 for irrigating an eye during a surgical procedure (as shown in FIG.1). In one example, the sterile fluid is a saline fluid, however, otherfluids may be used. At least a portion of the irrigation line 1140 maybe formed of a flexible tubing, and in some embodiments, the path 1140is formed of multiple segments, with some segments being rigid andothers being flexible.

The irrigation pressure sensor 1130 is associated with the irrigationline 1140 and performs the function of measuring the irrigation pressurein the irrigation line 1140. In some embodiments, the sensor 1130 is apressure sensor configured to detect current pressure conditions. Thesensor 1130 communicates signals indicative of the sensed pressure tothe controller 1230. Once received, the controller 1230 processes thereceived signals to determine whether the measured pressure is above orbelow a desired pressure or within a pre-established desired pressurerange. Although described as a pressure sensor, the irrigation pressuresensor 1130 may be another type of sensor, such as a flow sensor thatdetects actual fluid flow and may include additional sensors formonitoring additional parameters. In some embodiments, the sensor 1130includes its own processing function and the processed data is thencommunicated to the controller 1230.

The aspiration line 1155 extends from the hand piece to the drainreservoir 1180 (as shown in FIG. 1). The aspiration line 1155 carriesaway fluid used to flush the eye as well as any emulsified particles.

The aspiration pressure sensor 1160 is associated with the aspirationline 1155 and performs the function of measuring the waste fluidpressure in the aspiration line 1155. Like the sensor 1130 describedabove, the sensor 1160 may be a pressure sensor configured to detectcurrent pressure conditions. It communicates signals indicative of thesensed pressure to the controller 1230. The sensor 1160, like the sensor1130, may be any suitable type of sensor, such as a flow sensor thatdetects actual fluid flow and may include additional sensors formonitoring additional parameters.

The hand piece 1145 may be an ultrasonic hand piece that carries theirrigation fluid to the surgical site. The hand piece is configured asknown in the art to receive and operate with different needles orequipment depending on the application and procedure being performed. Itshould be noted that although an ultrasonic hand piece is discussed, theprinciples of the invention are intended to cover the use of vitrectomycutter hand pieces or other hand pieces known in the art. For ease ofreference only, this application will refer only to the hand piece 1145,recognizing that the system operates in a similar manner with other handpieces.

In the example shown, the fluid command input device 1210 is typically afoot pedal. It can receive inputs indicative of a desired flow rate,desired pressure, or other fluid characteristic. It is configured tocontrol the operational setting of the machine through a plurality ofmajor control settings, including controlling the irrigation flow rateor pressure within each of the major control settings. In someembodiments, the flow command input device is not a foot pedal, but isanother input device, located elsewhere on the machine.

The controller input device 1240 permits a user to enter data orcommands that affect system programming. In this embodiment, thecontroller input device 1240 is associated with the display 1220.However, it could be associated directly with the controller in a mannerknown in the art. For example, in some embodiments, the controller inputdevice 1240 is a standard computer keyboard, a standard pointing device,such as a mouse or trackball, a touch screen or other input device.

As is apparent from FIG. 5, the controller 1230 communicates with thedisplay 1220, the flow command input device 1210, the hand piece 1150,the irrigation pressure sensor 1130, the aspiration pressure sensor1160, and the controller input device 1240. It is configured orprogrammed to control the pressurized irrigation system based uponpre-established programs or sequences.

In use, the controller 1230 is configured to receive signals from theirrigation pressure sensor 1130 and process the signals to determinewhether the detected irrigation pressure is outside of an acceptablerange or above or below acceptable thresholds. If the controller 1230detects an unacceptable irrigation pressure, it controls the pressurizedirrigation system to correct the pressure to a desired range. Likewise,in another example, the controller 1230 is configured to receive signalsfrom the aspiration pressure sensor 1160 and process the signals todetermine whether the detected pressure is outside of an acceptablerange or above or below acceptable thresholds. If the controller 1230detects an unacceptable pressure, it controls the pressurized irrigationsystem to correct the pressure to a desired range. In this manner, theirrigation pressure sensor 1130 and/or the aspiration pressure sensor1160 may be used to control the fluid pressure in the eye (IOP).

Returning to FIG. 1, aspiration pressure sensor 1160 measures thepressure in the aspiration line 1155 or aspiration pathway. Aspirationpressure sensor 1160 may be located anywhere along the aspiration line1155 or aspiration pathway. If located close to the eye 1145, aspirationpressure sensor may be located in the hand piece 1150. Aspirationpressure sensor 1160 is implemented by any of a number of commerciallyavailable fluid pressure sensors. Aspiration pressure sensor 1160provides pressure information to a controller (shown in FIG. 5) thatoperates pressurized irrigation fluid source 1105.

A hand piece 1150 is placed in the eye 1145 during a phacoemulsificationprocedure. The hand piece 1150 has a hollow needle that isultrasonically vibrated in the eye to break up the diseased lens. Asleeve located around the needle provides irrigation fluid fromirrigation line 1140. The irrigation fluid passes through the spacebetween the outside of the needle and the inside of the sleeve. Fluidand lens particles are aspirated through the hollow needle. In thismanner, the interior passage of the hollow needle is fluidly coupled toaspiration line 1155. Pump 1170 draws the aspirated fluid from the eye1145. An aspiration pressure sensor 1160 measures the pressure in theaspiration line. An optional vent valve can be used to vent the vacuumcreated by pump 1170. The aspirated fluid passes through reservoir 1175and into drain bag 1180.

During a phacoemulsification procedure, the tip of the needle on handpiece 1150 may become occluded with a lens particle. This creates acondition that is called an occlusion. During an occlusion, less fluidis generally aspirated from the eye, and the vacuum pressure inaspiration line 1155 increases as a result of the occlusion.Accordingly, during an occlusion, aspiration pressure sensor 1160detects the increased vacuum that is present in aspiration line 1155.When the occlusion breaks (that is when the lens particle that causesthe occlusion is broken up by the ultrasonic needle), a surge occurs.The increased vacuum in aspiration line 1155 creates a sudden demand forfluid from the eye resulting in a rapid lowering of IOP and shallowingof the operating space within the eye. This can lead to a dangeroussituation in which various structures of the eye can be damaged.

Upon occlusion break, the aspiration pressure sensor 1160 detects a dropin pressure in aspiration line 1155. Likewise, the irrigation pressuresensor 1130 also detects the pressure drop in irrigation line 1140 thatoccurs as a result of occlusion break. Signals from the irrigationpressure sensor 1130 and/or the aspiration pressure sensor 1160 may beused by the controller 1230 to control the irrigation source 1105 asmore thoroughly described below.

The pressurized irrigation system of the present invention is capable ofresponding to the surge caused by occlusion break by increasing theirrigation pressure in irrigation line 1140. When an occlusion breaksand a surge occurs, pressurized irrigation fluid source 1105 increasesthe pressure of the irrigation fluid in response. Increasing theirrigation pressure of pressurized irrigation fluid source 1105 meetsthe added fluid demand caused by occlusion break. In this manner, thepressure and resulting operating space in eye 1145 can be maintained ata relatively constant value which may be selected by the surgeon.

Likewise, when an occlusion occurs, irrigation pressure may increase asthe fluid aspirated from the eye decreases. An increase in irrigationfluid pressure detected by irrigation pressure sensor 1130 can be usedto control pressurized irrigation fluid source 1105 to regulate thepressure in eye 1145—that is to keep the pressure in eye 1145 within anacceptable range. In such a case, the aspiration pressure sensor 1160may also detect the presence of an occlusion and a reading from it maybe used by controller 1230 to control pressurized irrigation source1105. In this case, the pressure in pressurized in pressurizedirrigation fluid source 1105 is not increased but remains the same or isdecreased.

Generally, control of the pressurized irrigation fluid source 1105 isbased on two parameters: (1) a pressure reading and (2) an estimate ofirrigation flow based on flow through the system (or a measurement ofactual flow through the system). The pressure reading may be from theirrigation pressure sensor 1130 (i.e. pressure in the irrigation line),the aspiration pressure sensor 1160 (i.e. pressure in the aspirationline) or the source pressure sensor 1110 (i.e. pressure at thepressurized irrigation source).

In one embodiment of the present invention, control of the pressurizedirrigation fluid source 1105 can be based on irrigation pressure andflow through the system as modified by the compensation factor (asdescribed in detail below). Irrigation pressure can be used to controlfor occlusion break and to maintain a constant IOP. Irrigation flow alsodetermines IOP. Flow through the system as modified by the compensationfactor (which equates to irrigation flow) can be used to control forincision leakage and sleeve compression. Collectively, these parameterscan be used to maintain a constant IOP during the procedure.

Estimated flow through the system is generally the fluid flow from thepressurized irrigation source 1105 through the irrigation line 1140,through the hand piece 1150, into the eye 1145, out of the eye 1145,through the hand piece 1150, through the aspiration line 1155 and intothe drain bag 1180. In operation, fluid may also be lost from the systemby leakage from the eye 1145 or the wound through which the needle ofthe hand piece 1150 is inserted (also called “incision leakage”). Inthis manner the total fluid flow in the system is equal to the fluidthat flows through the eye minus the fluid that is lost due to incisionleakage.

Estimated fluid flow may be based on a number of different calculations.For example, flow can be estimated by any of the following:

-   -   (1) A differential pressure measurement to calculate flow can be        based on an aspiration pressure sensor reading plus pump        impedance plus maximum vacuum attained by the aspiration pump.        Flow can be calculated by the difference between the measured        aspiration pressure at the aspiration pressure sensor 1160, the        maximum vacuum that can be created by the pump 1170, and the        pump impedance. The impedance of the pump 1170 is a known        parameter and the maximum vacuum that the pump creates can be        measured accurately as can the aspiration pressure (by the        aspiration pressure sensor 1160). In this manner, flow is        estimated by the difference in two pressures in the fluid path        and the impedance of that path. In this case, the two pressures        are the pressure measure by the aspiration pressure sensor 1160        and the maximum pressure achievable by the pump 1170. The        impedance in this example is the impedance of the pump 1170.    -   (2) A differential pressure measurement to calculate flow can be        based on the source pressure measured at the source pressure        sensor 1110, the irrigation pressure measured at the irrigation        pressure sensor 1130, and the impedance of the irrigation line        (or irrigation path) from the irrigation source 1105 to the        irrigation pressure sensor 1130. Flow can be calculated by the        pressure difference between the irrigation source 1105 and the        irrigation pressure sensor 1130 and the impedance of the        irrigation line 1140 between the irrigation source and the        irrigation pressure sensor. In this manner, flow is estimated by        the difference in two pressures in the fluid path and the        impedance of that path.    -   (3) When the pressurized irrigation fluid source 1105 is a        flexible bag 1109 located between two opposing plates 1106 and        1107 (as depicted in FIG. 2), the travel of plates 1106 and 1107        correspond to fluid flow through the system. Fluid flow and/or        the volume of fluid used during the procedure can be estimated        directly from the position of plates 1106 and 1107. Generally,        during a procedure, plates 1106 and 1107 travel toward each        other to squeeze fluid out of flexible bag 1109 at a desired        pressure or flow rate. The total fluid that exits the flexible        bag 1109 is directly related to the position of the opposing        plates 1106 and 1107. The closer plates 1106 and 1107 are        together, the more fluid has left the flexible bag 1109. In this        manner, the position of plates 1106 and 1107 can also be used to        indicate the amount of fluid left in the flexible bag 1109 and        provide an indication to the surgeon of the fluid level in the        flexible bag 1109 (for example, by displaying fluid level on the        display 1220).

Actual fluid flow through the system may also be affected by twodifferent factors: incision leakage and sleeve compression. As notedabove, the hand piece 1150 has a sleeve located around a needle. Thesleeve provides irrigation fluid from irrigation line 1140 to the eye1145. The irrigation fluid passes through the space between the outsideof the needle and the inside of the sleeve. Fluid and lens particles areaspirated through the hollow needle. During a procedure, the sleeve andneedle are inserted into the eye through a small incision. In thismanner, the sleeve contacts the eye tissue of the incision (or wound).Incision leakage describes the amount of fluid that exits the eyethrough the wound (or through the space between the sleeve and the eyetissue through which the wound is formed). During a procedure, fluid mayexit the eye through the wound—such fluid loss exits the system (i.e.the fluid that exits the eye does not pass through the aspiration line1155). Incision leakage typically results in the loss of a small amountof fluid thus decreasing the total flow through the system. Expressedmathematically, irrigation flow=aspiration flow+incision leakage.

Sleeve compression generally describes the condition in which the sleeveis pinched or compressed against the needle when inserted into theincision. Sleeve compression occurs more frequently with smallerincisions and may or may not result in less incision leakage. Sleevecompression can restrict fluid flow through the system. Since pinchingthe sleeve increases the flow resistance in the system, flow may bedecreased when sleeve compression is present.

Generally, the losses due to incision leakage and sleeve compression aredependent on the type of needle and sleeve that is being used as well assurgeon technique. Flow profiles for various combinations of needles andsleeves can be determined experimentally and the resulting dataincorporated into an algorithm or database for use in control ofpressurized irrigation fluid source 1105. Alternatively, suchexperimental data can be aggregated to provide a range of differentcompensation factors (as described in the next paragraph). Surgeontechnique differs considerably among the population of ophthalmologists.During a procedure, some surgeons may move the needle in a manner thatcreates more sleeve compression. Surgeons also prefer different sizes ofneedles and sleeves as well as different incision sizes. These surgeonspecific factors also impact incision leakage and sleeve compression.

A compensation factor may be implemented to compensate for these twodifferent variables that result in a decrease in flow through thesystem: incision leakage and sleeve compression. Incision leakage may becompensated with an estimated incision leak rate factor (which can beimplemented as an offset that is set as a default value). Sleevecompression may be compensated with an estimated compression factor. Theincision leak rate factor and the sleeve compression factor maycollectively comprise the compensation factor. The compensation factormay be surgeon-adjustable. The compensation factor may be an offset thatacts to either increase or decrease the pressure at the pressurizedirrigation fluid source 1105. For example, the compensation factor maybe an integer from zero to seven (with zero being no compensation andseven being maximum compensation).

Irrigation flow can be estimated from the estimated flow through thesystem and the compensation factor. Since irrigation flow generallyequals aspiration flow plus incision leakage. Therefore, irrigationpressure can be estimated from the compensation factor and estimatedflow through the system.

Generally, in order to compensate for the decreased flow (or losses)resulting from incision leakage and sleeve compression, the pressure inpressurized irrigation fluid source 1105 is increased slightly. Suchincrease in pressure may be implemented in an algorithm based on thecompensation factor. In the above example, a surgeon may select acompensation factor of three to provide moderate compensation forincision leakage and sleeve compression. In this example, a compensationfactor setting of three may correspond to a slight increase in pressureat the pressurized irrigation fluid source 1105. In other words, thebaseline pressure at the pressurized irrigation fluid source 1105 isincreased slightly to compensate for these factors.

In another example, the compensation factor may be implemented by adefault offset value that can be adjusted by the surgeon. A nominalconstant may be the default offset value in the algorithm. The surgeonmay adjust this default value by a factor (of between zero for nocompensation and 2 for double the compensation). The default offsetvalue can be determined by the experimental data relating to flowcharacteristics of various needle and sleeve combinations. Some needleand sleeve combinations are much more common than others, so that themost common combinations may be used to determine the default offsetvalue. In other instances, an aggregation of this data may be used todetermine the default offset value.

In another example, the surgeon may enter the type of sleeve and needlevia controller input device 1240. A bar code reader may be employed toscan the bar code from the surgical pack that includes the sleeve andneedle as well. When the controller 1230 receives the needle and sleeveinformation, it can determine the flow characteristics associated withneedle and sleeve (or look up the flow characteristics from a database)and select an appropriate compensation factor. In addition, doctorpreferences and/or data from prior procedures can be used to select theproper compensation factor. For example, parametric data from priorprocedures may be used to determine doctor technique and adjust, modify,or select the compensation factor.

Regardless of how the compensation factor is determined, thecompensation factor may be used to compensate for flow losses. Thecompensation factor may be used to control the pressurized irrigationfluid source 1105 so as to provide an amount of fluid equal to thatfluid lost due to incision leakage. The compensation factor may be usedto control the pressurized irrigation fluid source 1105 so as to providea slight increase in pressure to overcome the increased flow resistancecaused by sleeve compression. In addition, since irrigation flowdetermines IOP, the compensation factor is used to adjust IOP as well asto compensate for flow losses.

Therefore, control of the pressurized irrigation fluid source 1105 canbe based on irrigation pressure and flow through the system as modifiedby the compensation factor. Irrigation pressure can be used to controlfor occlusion break and to maintain a relatively constant IOP. Flowthrough the system as modified by the compensation factor can be used tocompensate for incision leakage and sleeve compression and maintain arelatively constant IOP. Collectively, these parameters can be used tomaintain a relatively constant IOP during the procedure.

The estimation of IOP may be based on the irrigation pressure sensor.The pressure drop between the irrigation pressure sensor and the eye isknown because the characteristics of the passage between the irrigationpressure sensor and the eye are known. For example, if the irrigationpressure sensor is located in a fluidics cassette that is connected tothe hand piece 1150 through a length of irrigation line 1140, then theflow impedance of the length of irrigation line 1140 and the irrigationpathway through the hand piece 1150 are both known (or can be measured).IOP can then be determined from the irrigation pressure sensor reading.The TOP reading may also be affected by sleeve compression (because thesleeve is in the irrigation path between the irrigation pressure sensorand the eye) and incision leakage. The compensation factor may be usedto adjust IOP for these losses (or changes in the impedance).

In one embodiment of the present invention, a surgeon selects a desiredIOP. The pressurized irrigation fluid source 1105 is then controlled tomaintain the desired IOP. Since IOP is based on a reading from theirrigation pressure sensor, the irrigation pressure sensor 1130 can beused to control the pressurized irrigation fluid source 1105. Inconjunction with irrigation pressure, flow through the system asmodified by the compensation factor can also be used to control thepressurized irrigation fluid source 1105. Irrigation flow alsodetermines IOP. The flow through the system as modified by compensationfactor equates to irrigation flow. When an occlusion is present (asdetected by the irrigation pressure sensor 1130 or the aspirationpressure sensor 1160), IOP can be maintained by this control scheme. Onocclusion break (as detected by the irrigation pressure sensor 1130 orthe aspiration pressure sensor 1160), the pressurized irrigation fluidsource 1105 can be controlled to maintain a relatively constant IOP.

Alternatively, source pressure sensor 1110 or aspiration pressure sensor1160 may be used in place of irrigation pressure sensor 1130 in thecontrol scheme above.

The control of pressurized irrigation fluid source 1105 can also bedescribed in three different states: steady state (when the needle isnot occluded and flow through the system is relatively constant);occluded state (when the needle is occluded and there is little or noflow through the system); and occlusion break or surge (when there is asudden and rapid flow through the system). An example of each state isdescribed.

For example, in steady state, the pressurized irrigation fluid source1105 is controlled to maintain a selected IOP. The irrigation pressuresensor 1130 is used to provide an estimate of IOP. A pressure readingfrom irrigation pressure sensor 1130 is received by the controller 1230.The desired IOP is also received by the controller 1230. The controllerdirects the operation of pressurized irrigation fluid source 1105 so asto maintain the desired IOP. In steady state, the controller typicallydirects pressurized irrigation fluid source 1105 to provide fluid at arelatively constant pressure to maintain IOP. In addition, thecontroller calculates a value for estimated fluid flow as modified bythe compensation factor. In this example, in steady state, flow may beestimated by a differential pressure measurement or by plate travel. Inthe case of a differential pressure measurement, the controller 1230receives the pressure reading(s) needed for the differential pressuremeasurement and makes the calculation. In the case of plate travel, thecontroller 1230 receives readings from position sensors or the like anddetermines plate travel. The compensation factor is also received by thecontroller (as an input by the surgeon, for example). Since irrigationfluid flow (estimated flow through the system as modified by thecompensation factor) is related to IOP, the controller 1230 directs theoperation of pressurized irrigation fluid source 1105 to maintain a flowrate consistent with the desired IOP. The net result is that thecompensation factor is used to adjust fluid pressure at the pressurizedirrigation fluid source 1105 to compensate for flow losses.

When an occlusion occurs, the tip of the needle is wholly or partiallyclogged with a lens particle. In the occluded state, flow through thesystem is decreased. The irrigation pressure sensor 1130 provides anestimate of IOP. A pressure reading from irrigation pressure sensor 1130is received by the controller 1230. The desired IOP is also received bythe controller 1230. The controller directs the operation of pressurizedirrigation fluid source 1105 so as to maintain the desired IOP. In anoccluded state, the controller typically directs pressurized irrigationfluid source 1105 to provide fluid at a relatively constant pressure tomaintain IOP. Maintaining pressure in an occluded state is likely tomean that the plates 1106 and 1107 maintain the flexible bag 1109 at arelatively constant pressure. In addition, the controller calculates avalue for estimated fluid flow as modified by the compensation factor asdetailed above. Since irrigation fluid flow (estimated flow through thesystem as modified by the compensation factor) is related to IOP, thecontroller 1230 directs the operation of pressurized irrigation fluidsource 1105 to maintain a flow rate consistent with the desired IOP. Thenet result is that the compensation factor is used to adjust fluidpressure at the pressurized irrigation fluid source 1105 to compensatefor flow losses (e.g. incision leakage).

When an occlusion break occurs, the lens particle at the tip of theneedle is dislodges and a surge of fluid exist the eye through the lumenof the needle. During occlusion break, flow through the system isincreased. The irrigation pressure sensor 1130 provides an estimate ofIOP. A pressure reading from irrigation pressure sensor 1130 is receivedby the controller 1230. The desired IOP is also received by thecontroller 1230. The controller directs the operation of pressurizedirrigation fluid source 1105 so as to maintain the desired IOP. Duringocclusion break, the controller typically directs pressurized irrigationfluid source 1105 to provide fluid at an increased pressure to maintainIOP. Maintaining pressure during occlusion break is likely to mean thatthe plates 1106 and 1107 exert force on the flexible bag 1109 toincrease the pressure in the irrigation line so as to provide thenecessary fluid flow to meet the fluid demand of the surge. In addition,the controller calculates a value for estimated fluid flow as modifiedby the compensation factor as detailed above. Since irrigation fluidflow (estimated flow through the system as modified by the compensationfactor) is related to IOP, the controller 1230 directs the operation ofpressurized irrigation fluid source 1105 to maintain a flow rateconsistent with the desired IOP. The net result is that the compensationfactor is used to adjust fluid pressure at the pressurized irrigationfluid source 1105 to compensate for flow losses (e.g. incision leakage).

In a further embodiment of the present invention, incision leakage maybe determined as the difference between irrigation fluid flow andaspiration fluid flow. Irrigation fluid flow can be measured directlywith a flow sensor, can be calculated using a differential pressuremeasurement, or can be calculated based on plate travel. Readings fromthe source pressure sensor 1110 and the irrigation pressure sensor 1130can be used to make a differential pressure measurement. In this case,the flow impedance between the source pressure sensor 1110 and theirrigation pressure sensor 1130 is known (or can be measured). Thedifference in the pressure readings measured by the source pressuresensor 1110 and the irrigation pressure sensor 1130 can be calculatedand flow determined. In the case of plate travel, flow can be estimatedfrom the position and/or movement of the plates 1106 and 1107.

Aspiration fluid flow can also be calculated using a differentialpressure measurement. Flow can be calculated by the difference betweenthe measured aspiration pressure at the aspiration pressure sensor 1160,the maximum vacuum that can be created by the pump 1170, and the pumpimpedance. The impedance of the pump 1170 is a known parameter and themaximum vacuum that the pump creates can be measured accurately as canthe aspiration pressure (by the aspiration pressure sensor 1160). Inthis manner, flow is estimated by the difference in two pressures in thefluid path and the impedance of that path. In this case, the twopressures are the pressure measure by the aspiration pressure sensor1160 and the maximum pressure achievable by the pump 1170. The impedancein this example is the impedance of the pump 1170.

Using the calculated values for irrigation flow and aspiration flow, onecan find incision leakage as the difference between irrigation flow andaspiration flow. This calculation of incision leakage may then be usedto more accurately determine the compensation factor. In one embodimentof the of the present invention, the compensation factor is determineddynamically based in part on the calculated incision leakage.

Finally, it should be noted that the position of plates 1106 and 1107may be used to indicate the volume of fluid used during the procedureleft in the flexible bag 1109. As noted above, the relative position ofopposing plates 1106 and 1107 indicates the volume of fluid that hasexited the flexible bag 1109. In some cases, a new bag of irrigationfluid may need to be installed in pressurized irrigation fluid source1105 if the existing flexible bag 1109 is low on fluid. Since therelative position of the opposing plates 1106 and 1107 indicates thevolume of fluid used, and since the total volume of fluid in flexiblebag 1109 is known, these two parameters can be used to provide anindication to the surgeon of the fluid level in the flexible bag 1109(for example, by displaying fluid level on the display 1220). If thefluid level is low, a warning can be given to the surgeon so that a newflexible bag 1109 of fluid can be installed in pressurized irrigationfluid source 1105.

From the above, it may be appreciated that the present inventionprovides an improved phacoemulsification system. The present inventionprovides active control of pressure in the eye during the surgicalprocedure. The present invention is illustrated herein by example, andvarious modifications may be made by a person of ordinary skill in theart.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A surgical system comprising: a pressurizedirrigation fluid source; an irrigation line fluidly coupled to thepressurized irrigation fluid source; a hand piece fluidly coupled to theirrigation line; an irrigation pressure sensor located at or along thepressurized irrigation fluid source or irrigation line; and a controllerfor controlling the pressurized irrigation fluid source; wherein thecontroller controls the pressurized irrigation fluid source based on areading from the irrigation pressure sensor and an estimated flow valuemodified by a compensation factor.
 2. The surgical system of claim 1wherein the compensation factor is based on incision leakage.
 3. Thesurgical system of claim 1 wherein the compensation factor is based onsleeve compression.
 4. The surgical system of claim 1 furthercomprising: a display; and a controller input device.
 5. The surgicalsystem of claim 4 wherein the controller input device receives a desiredintraocular pressure value and the controller controls the pressurizedirrigation fluid source so as to maintain the desired intraocularpressure value.
 6. The surgical system of claim 4 wherein the controllerinput device receives a desired intraocular pressure range and thecontroller controls the pressurized irrigation fluid source so as tomaintain the desired intraocular pressure range.
 7. The surgical systemof claim 1 wherein the controller calculates intraocular pressure of aneye based on the reading from the irrigation pressure sensor.
 8. Thesurgical system of claim 1 wherein the controller calculates intraocularpressure of an eye based on the estimated flow value modified by thecompensation factor.
 9. The surgical system of claim 1 furthercomprising: an aspiration line fluidly coupled to the hand piece; anaspiration pressure sensor located at or along the aspiration line; andan aspiration pump configured to draw fluid through the aspiration line.10. The surgical system of claim 9 wherein the controller calculates theestimated flow value based on a reading from the aspiration pressuresensor, a maximum pump vacuum achievable by the aspiration pump, and animpedance of the aspiration pump.
 11. The surgical system of claim 1further comprising a source pressure sensor for measuring a pressure ofthe pressurized irrigation fluid source.
 12. The surgical system ofclaim 11 wherein the controller calculates the estimated flow valuebased on a reading from the irrigation pressure sensor, the sourcepressure sensor, and an impedance of the irrigation line.
 13. Thesurgical system of claim 1 wherein the pressurized irrigation fluidsource comprises: a flexible bag holding a fluid; and two opposingplates; the flexible bag located between the two opposing plates. 14.The surgical system of claim 13 wherein the controller calculates theestimated flow value based on travel or motion of the two opposingplates.
 15. The surgical system of claim 1 wherein the compensationfactor is based on a needle and sleeve selected for a procedure.
 16. Thesurgical system of claim 4 wherein the controller input device receivesa compensation factor from a user.
 17. The surgical system of claim 4wherein the controller input device receives needle and sleeveinformation and the controller uses the needle and sleeve information toselect or calculate the compensation factor.
 18. The surgical system ofclaim 17 wherein the controller selects or calculates the compensationfactor based on fluid flow characteristics of a needle and sleevecombination.
 19. The surgical system of claim 11 wherein the controllercalculates intraocular pressure of an eye based on a reading from thesource pressure sensor.
 20. The surgical system of claim 9 wherein thecontroller uses a reading from the aspiration pressure sensor todetermine if an occlusion is present or if an occlusion break occurs.21. The surgical system of claim 20 wherein the controller controls thepressurized irrigation fluid source to accommodate for changes in fluidflow that result from the occlusion or the occlusion break.
 22. Thesurgical system of claim 1 wherein the controller uses a reading fromthe irrigation pressure sensor to determine if an occlusion is presentor if an occlusion break occurs.
 23. The surgical system of claim 22wherein the controller controls the pressurized irrigation fluid sourceto accommodate for changes in fluid flow that result from the occlusionor the occlusion break.
 24. A surgical system comprising: a pressurizedirrigation fluid source, the pressurized irrigation fluid sourcecomprising a flexible bag located between two opposing plates, theflexible bag containing a fluid; a position sensor located at or on oneof the two opposing plates, the position sensor for determining adistance between the two opposing plates; an actuator for moving atleast one of the two opposing plates so as to squeeze the flexible bag;and a controller for controlling the relative movement of the opposingplates; wherein the controller receives reading from the positionsensor, determines the distance between the plates, and provides anestimate of an amount of fluid in the flexible bag.
 25. The surgicalsystem of claim 24 further comprising a display.
 26. The surgical systemof claim 25 wherein an indication of the amount of fluid in the flexiblebag is displayed on the display.
 27. The surgical system of claim 25wherein an indication of a low fluid level is displayed on the display.28. The surgical system of claim 24 wherein the controller initiates awarning when the amount of fluid in the flexible bag is below a value.29. A surgical system comprising: a pressurized irrigation fluid source,the pressurized irrigation fluid source comprising a flexible baglocated between two opposing plates, the flexible bag containing afluid, a hinged plate located on a surface of one of the two opposingplates; and a source pressure sensor located between a face of thehinged plate and a face of one of the two opposing plates, such that theface of the hinged plate presses the source pressure sensor against theface of one of the two opposing plates.
 30. The surgical system of claim29 further comprising: a controller for receiving a reading from thesource pressure sensor.